A fio output taken from the raid1 cfq (2.6.28.1-patch 1) run looks likethe following. It's a bit strange that we have readers started earlierwhich seems to complete only _after_ more recent readers have.

Given the numbers I get, I see that runt-max numbers does not appear tobe so high at each job file run, which makes it difficult to comparethem (since you never know if you've hit the worse-case yet). This couldbe related to raid1, because I've seen this both with and without yourpatch applied, and it only seems to appear on raid1 executions.

However, the patch you sent does not seem to improve the behavior. Itactually makes the average and max latency worse in almost every case.Changing the queue, slice_async_rq and quantum parameters clearly helpsreducing both avg and max latency.